1. Field of the Invention
The present invention concerns an arrangement and a reference means for the precision aiming of a radiation beam for treating an internal cancer tumor.
2. Description of Related Art
During the last 40 years, radiation therapy of localized prostate cancer has been used as one of a number of treatment methods. The levels of radiation considered suitable for treatment fall within the interval 65-70 Gy. However, the occurrence of viable cancer cells even after such a level of treatment has been demonstrated. One way of dealing with these remaining cells is to increase the level of treatment, known as scaling up the dose, initially to the interval of 76-80 Gy or more.
However, because of the lack of precision of current techniques, radiation treatment also carries with it an increased risk of affecting organs adjacent to the tumor. In the area around the prostate, this means primarily an increased risk for side effects seen as damage to the rectum and the urinary bladder as these are normally found in the radiation field. The risk for damage is especially pronounced with high doses of radiation.
The preparations for the radiation treatment of prostate cancer can be described briefly in the following way. The patient undergoes computer tomography to determine the geometry and location of the prostate. The position of the prostate is shown by markings on the skin of the patient. These markings then constitute the directional points for the beams used in treatment.
Even if the geometry of the prostate is known, problems can arise during radiation treatment because the position of the prostate is not constant in relation to the pelvis or, for that matter, to the skin where the markings have been made. The patient""s subcutaneous fat means that the markings can be displaced in relation to the pelvis, and different muscle contractions, such as those in the area around the prostate, can displace the prostate up to one centimeter in relation to the pelvis. Furthermore, variation in the contents of the intestine and the bladder can affect the position of the prostate. When added together, this has the effect that the field of radiation must have a margin of 1.5-2 cm around the determined position of the prostate, which means that the rectum and bladder can be subjected to radiation, thus limiting the possibility of giving very high doses of radiation.
Even though the problem has initially been described in connection with the treatment of prostate cancer, it should be emphasised that many aspects of the problem are common to the treatment of cancer tumors in other organs. This is especially true for tumors of the cervix, urinary bladder, stomach, intestinal tract, pancreas, mouth, throat, etc.
During radiation therapy, a treatment beam is emitted from equipment used for the treatment. Depending on the shape of the object to be treated, a cross-section of the treatment beam is chosen so that the treatment is restricted to a specified treatment area. If the treatment area is to be reduced to a size approximately the size of the object to be treated, it is of great importance that the beam strikes its target, the tumor, with great precision.
One objective of the present invention is to achieve the precise aiming of the direction of a treatment beam during the radiation treatment of internal cancer tumors so that the margins of the treatment beam can be reduced, thereby minimizing the effect on adjacent organs and tissue.
This objective is achieved with an arrangement and a reference device including equipment for emitting a treatment beam, a sight arranged in the path of the beam and a device to read the location of a sight relative to a reference marker located in the patient.
By using the invention, it is possible to describe the geometry of an organ based on one or more reference points that always occupy the same position with reference to the organ. In addition, the possibility to repeatedly direct the treatment beam with precision in relation to at least one said reference point so that the beam always strikes the cancer tumor with precision, is also achieved. As such, the beam does not need as large a safety margin as has been required until now, but can be assigned a profile that is more or less exactly identical with that of the object to be treated.
Before each treatment occasion, it is thus possible to check, adjust and verify that the cancer tumor really is in the path of the treatment beam.
Additional features and advantages of the invention will be made evident by the following detailed description of one preferred embodiment of the invention, which constitutes one example and as such does not limit the area of protection of the invention. Embodiments of the invention have further applications within general internal radiation treatment of cancer, as will be made evident below. To simplify understanding, the text contains references to the enclosed drawings, in which equivalent or similar parts are assigned the same designation.